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wire routing thoughts - jcassity - 04-01-2017

I noticed in my 46-1226 oem repair manual information that there is specific wires called out to be routed in a particular manner.

Routed meaning to avoid things like heat or static generation or humming etc.
The information mentions to route the wiring along the outter perimeter of the chassis away from tube sockets and   other items.

I was planning to take all the cob web of wires out and replace with longer or shorter runs so i end up with a bundled wire harness along the chassis , and at the logical point, break out the individual conductors and send them to the termination point.

What i want to do is look down into the bottom of the chassis and see a neatly groomed and fanned out harness.

is this overkill,  is there any net gain in doing it like this ?

I suppose what will end up happening in most all cases is each conductor will be much longer than original, and with that said, is this a bad thing? 

as i stare down into the chassis and especially at the 4 tier waffer band selector switch it appears there was a great effort put into making the wire as short as possible ,,,

it makes me ask this question,, is shorter wires better in these radios for some "engineered" reason?

RE: wire routing thoughts - morzh - 04-01-2017

Do not improve on original roting, it was there for a reason. Just replicate what was there before.
PS. Lengthening conductors is almost always a bad thing.

RE: wire routing thoughts - David - 04-01-2017

Please put them back in the exact place. Take pictures and draw out the location of each wire, in the past failed to do this and had lots of hum. No fun rewiring a radio twice. If I find wires  that I want to replace will do all other work first place tape over bad spots see how it plays then start replacing wires. If you have a lot of rotten insulation you will need to replace them first and hope for the best. David

RE: wire routing thoughts - Mondial - 04-01-2017

You definitely do not want to lengthen or change the position of wires, especially in the band switch area. 

At short wave frequencies, a length of wire acts as an inductor or coil and placing two wires next to each other forms a capacitor. At VHF, one inch of wire may change the tuning of the circuit completely. So at these frequencies you are changing the actual circuit design by changing the physical wiring.

At audio frequency, this effect is not as significant, but bundling a low level audio amp grid circuit wire with filament wiring will definitely cause hum. Placing the same grid wire next to plate wiring of the following stage will cause it to go into squealing oscillations.

The original wiring was placed as it was for a reason, and the engineers involved spent a great deal of time and effort getting it right. It may not be pretty, but the wiring layout was done for best operation and performance. 

That's why the repair info says to duplicate it as closely as possible.

RE: wire routing thoughts - jcassity - 04-01-2017

interesting comments,

I had suspected that they wouldnt have built such a cob web just for the sake of saving costs on wire.

I am glad i asked this question though,, i was about to "think" i could make it a better looking sestup and improve on access to components.

i just now got the band selector out ,, yes i am documenting everything. VERY VERY VERY tight banjo strung parts.

I had no choice, i had to remove the BS Sw in order to gain access to V1 and 3 associated paper caps.

I wasnt about to spend the time to replace 2 dozen caps and leave these three alone.

RE: wire routing thoughts - Arran - 04-02-2017

With regards to how the wiring is routed under a chassis, yes it can make a difference. I had a Sparton AC/DC set that had a hum that would not go away, and after ruling out all of the usual suspects I noticed that some of the filament circuit wiring was routed parallel to the AVC wiring, so I rerouted the length of AVC wiring that was next to the heater wiring and solved the problem. It isn't often that the factory would make a mistake like this but in this case they did, as a rule anything with AC running through it is usually routed as close to the chassis as possible and as far away from the AVC or audio circuit wiring as possible as not to induce hum.
Regards
Arran